The present invention relates to imaging apparatus, and more particularly relates to an imaging apparatus capable of rapidly generating an optionally-sized, reduced image from a high-resolution image sensor.
Because of the spreading of personal computers in recent years, there is an increasing demand for digital cameras as an image pickup equipment. Also, high-quality digital camcorders are widely used as recording equipment of a movie.
Among the several factors that determine the image quality of the above described digital camera, the number of pixels of image sensor is a major factor for determining resolution. For this reason, some digital cameras are sold in the recent market as having even a large number of pixels of 4,000,000 or more.
For some use of photographed images, however, a high-definition image data having a large number of pixels is not necessarily required. For example, one having a reduced pixel size is more likely to be used as the image to be displayed at Web sites on the Internet. Further, as an added function for digital camera, a sequence of images of the same object can be taken with instantaneously varying the image taking condition so as to save only those of excellent results.
In this case, however, while pictures must be taken in rapid succession, not so many of those digital cameras having a large number of pixels are capable of taking images in rapid succession as bottlenecked by the flashing time from the image sensor to image memory. Further, since taking of a movie by a digital camera is also demanded, transmission to the memory in any case must be performed rapidly. It is preferable to previously reduce the amount of data to be processed.
On the other hand, when image size is to be reduced in conventional size reducing techniques based on linear interpolation, all pixels are used at first to form a large size image and then a smaller size image is formed by a linear interpolation. FIGS. 1 and 2 illustrate the techniques for generating a full-color reduced image by sampling of bilinear interpolation and bi-cubic interpolation, respectively, from Bayer-matrix image.
In the case based on the sampling of bilinear interpolation shown in FIG. 1, a full-color data of point A, B, C, D, is computed from a total of 12 points of R, G, B data in its vicinity. For example, linear combinations of R43, R45, R63, R65, B34, B36, B54, B56, G44, G53, G55, G64, are used for point A, and linear combinations of R03, R05, R23, R25, B14, B16, B34, B36, G15, G24, G26, G35 for point B. Similar linear combinations are used also for points C, D.
In the case based on the sampling of bi-cubic interpolation shown in FIG. 2, on the other hand, the linear combinations for point B for example use a total of 48 points: R61, R63, R65, R67, R01, R03, R05, R07, R21, R23, R25, R27, R41, R43, R45, R47, B72, B74, B76, B70, B12, B14, B16, B10, B32, B34, B36, B30, B52, B54, B56, B50, G75, G04, G06, G13, G15, G17, G22, G24, G26, G20, G33, G35, G37, G44, G46, and G55.
Although such techniques for generating a reduced image by linear interpolation provide an excellent image quality, there is a disadvantage of slow operation due to the fact that the linear interpolation is performed by fetching all pixel data. This is unfavorable as described above in the function for taking a multiple of images in rapid succession or when taking a movie.
Among the techniques for reducing the amount of read out data to be transmitted to the memory as described, methods are known to add an integrating function to the image sensor so that a reduced image is generated by reading a smaller number of averaged data. Japanese Patent Application Laid-Open Number 2001-245141 discloses an image reducing method using advantage of such methods. In the technique disclosed in the above mentioned Japanese Patent Application Laid-Open Number 2001-245141, the original image on a single-image sensor incorporating Bayer matrix color filter array is formed into a three-sensor condition by separating it into R, G, B planes. An integration of pixel signals of each color in the three-sensor condition is performed in horizontal and vertical directions to change the size in each directions.
Among the averaging readout methods, a method is known in an image sensor using CCD to perform a concurrent readout of current values of plurality of pixels to shorten the total readout time. Use of this method, however, involves the problem of the overflow of capacity of transmission area which results in deterioration of signals. Further, a method for solving such problem in readout by CCD is the averaging of voltage readouts by capacitor device of CMOS as disclosed in Japanese Patent Application Laid-Open Number Hei-6-217201. Furthermore, Japanese Patent Application Laid-Open Number Hei-9-247689 suggests a technique in which averaging/thinning out sampling readout and all-pixel readout are switched between a movie and still image, revealing an advantage of improvement in the reading speed.